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Mazda’s rotary engine in the age of the electric car

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Re: Mazda’s rotary engine in the age of the electric car

#141

Post by ryukoposting »

486sx33 wrote: post #2

Does it produce more low end torque verses a traditional gasoline combustion engine? If not then why is it better suited for electrical generation? Is it more efficient with less load? The article mostly makes it sound like Mazda just loves the wankle and wants to find any possibly way to bring it back - even though it has “high” emissions… so coupling it with a hybrid electric motor makes it happen.. That can’t be t…

It has nothing to do with sentimentality.

Wankels have tremendous power-to-weight and power-to-size ratios. Their main problem is reliability. The generally accepted solution to improve rotary engine reliability (oil injection) results in poor emissions. The wide, flat-ish combustion chamber doesn't help the emissions problem, either.

The Wankel is at its most efficient and its most reliable when operating at a constant RPM. Conveniently, the EV generator application demands a pretty flat RPM band. As a result, the engine doesn't need to lean as hard into those emissions-increasing compromises.

Thus, EVs allow the Wankel's benefits over a reciprocating-piston engine to be reaped without the same costs as before. In theory, at least. It remains to be seen if the benefits will outweigh the drawbacks. I'm glad they're at least going to give it a try.

Re: Mazda’s rotary engine in the age of the electric car

#142

Post by jiveturkey »

pengaru wrote: post #105
jiveturkey wrote: post #18

Earlier quoted context omitted.

It's not a direct connection. You do want efficient horsepower to drive a generator. More low end torque means the HP comes at lower RPM, which should mean less fuel consumption. Sibling says the achilles heel of the Wankel rotary is low end torque, but you don't take the direct output from the engine, it goes through gear reduction for final drive output. The real achilles heel is the awful emissions. It's more or l…

The side-port exhaust used in the rx-8 generation RE substantially improved the emissions situation, but the fuel efficiency is still trash by modern ICE standards. It's been awhile since I gave a damn about wankels (or ICEs in general), but ISTR there being a relatively low limit to achievable static compression ratio due to the fundamental geometry of the swept volume. Modern ICE engines are largely exploiting the…

to the best of my knowledge, you are correct on all counts. the new rotary used as a generator does also have direct injection, but i don't think they gain much compression ratio from that, for the reasons you stated. it's more for efficiency. without reading up on it, i believe the combustion chamber mixture and flame front propagation is not great in a rotary (hence RX8 has 2 plugs per chamber, leading and trailing) and DI should improve on it.

Re: Mazda’s rotary engine in the age of the electric car

#143

Post by Cthulhu_ »

labcomputer wrote: post #118
jeremymims wrote: post #27

Earlier quoted context omitted.

This was how the BMW i3 worked. It was a rather novel design that included an optional small electric scooter motor in the rear that had a 2.5 gallon gas tank. When the battery was low, it would be charged by running the small generator. This was clearly a wonderful idea but it was hamstrung by a silly California rule requiring the gas range to be less than the electric range to qualify for rebates. With a 6 gallon t…

> it was hamstrung by a silly California rule requiring the gas range to be less than the electric range to qualify for rebates. The problem is that BMW wanted to get the same amount of credits as a pure-BEV. California anticipated that a car with 300 miles of gas range might spend much of it's life being driven on gas if there was no penalty for doing so... and in fact that is exactly what happened with many Europea…

> and in fact that is exactly what happened with many European plug-in hybrids sold as company cars.

The counter force to that is that lease car drivers have to meet certain fuel efficiency goals, so, adopt an efficient driving style and plug in the plug-in hybrid instead of ragging it around; I'm not sure what the consequences were though, probably more taxes. Either way, enough of a push for my colleagues with plug-in / hybrids to do the thing.

Re: Mazda’s rotary engine in the age of the electric car

#144

Post by dragontamer »

labcomputer wrote: post #138
dragontamer wrote: post #29

Earlier quoted context omitted.

> but an appropriate gear ratio should handle that. See Prius's "Powersplit Device". I'd describe the Powersplit device to be a combination of generator/alternator, starter/electric motor, reversed-differential (2x power inputs -> 1x driveshaft), and effective gear-ratio. All in one planetary gearset. EV motor2 determines the speed of the car. The ICE motor can spin at any speed that the computer determines to be use…

> I do think that the Prius (and Prius Prime) have surpassed the Volt's design, and the proof is in the pudding. Prius Prime has 52mpg, a figure far more efficient than the Volt ever had. This is partly because the Prius is optimized as a hybrid-first design, while the Volt is optimized as a BEV-first design. The difference is in the gear ratios of the planetary CVTs: Prius is optimized to minimize the amount of ener…

> However, that design is sub-optimal for a car that you want to act like an EV. As your link shows, the Prius must have the ICE spinning at speeds greater than 42 mph. Not a problem for a hybrid, but that doesn't work for a "range-extender EV" like the Volt. Additionally, (before the current model year) Toyota's plug-in hybrids can't provide full acceleration in EV mode--they always kick in the ICE when you floor it. That's again a consequence of how the transmission is optimized for hybrid operation.

True in 2007.

But 17 years later, the Prius Prime 2024 has 100% EV mode even at highway speeds. Toyota has improved the design since that webpage was made in 2007.

Despite this change, the Prius still achieves 57 mpg, even better than ever before.

Prius Prime is a proper EV-only mode, albeit a touch underpowered but its EV mode now covers all possible driving conditions.

------

I believe the modern Prius 2024 has 17,000 RPM limits now, as well as tweaked gear ratios and far larger EV and ICE engines. Despite the larger 220hp aggregate engine, the Prius remains absurdly efficient. Both in EV mode and in ICE mode.

This is why I was saying that the Volt has wasted it's opportunity. GM was ahead in many respects 10 years ago, but Toyota has caught up. The GM advantage has been squandered.

> By making compromises to the gasoline efficiency, GM was able to create a car which acts like a real EV most of the time: A 1st gen Volt will go at least 80 mph in EV mode, and won't turn on the ICE (come hell or high water) until the battery is below 5%. And, it will do that for an honest 35 miles of freeway driving.

Prius Prime added a button to enter EV-only mode in this 5th generation design starting in 2023.

It took Toyota too long to add this feature, but now that it's here the 5th generation Prius is a far better choice.

Especially because Prius still has it's trademarked 50+ MPG and 130+MPGe ratings. Top of the line efficiency.

It's somewhat frustrating to see Toyota catch up when GM was so far ahead for so long. Also because GM killed the Volt.

Re: Mazda’s rotary engine in the age of the electric car

#145

Post by londons_explore »

_yb2s wrote: post #104
user_7832 wrote: post #73

Earlier quoted context omitted.

Apparently they really don't scale well. I found this reddit post explaining it better: > Gas turbines scale extremely poorly. They rely on small clearance between the rotating blades and the housings for efficiency. The smaller the turbine, the greater the relative clearance and the more energy is lost. Gas turbines, at least with established technology, make very little sense below 300ish HP. As a real life compari…

Thank you, I've wondered for years why we didn't have tiny gas turbine engines...

I still believe it's possible - for example by having all the blades enclosed in a ring you can avoid gas escaping 'round' the blade.

And with metal 3d printers rapidly falling in price, I think it will get within the scope of university students to prototype soonish.

Re: Mazda’s rotary engine in the age of the electric car

#146

Post by londons_explore »

philwelch wrote: post #129
elevatedastalt wrote: post #92

Earlier quoted context omitted.

The reason jet engines have that sort of exhaust is because the primary purpose of the gas turbine there is to dump all the excess energy into the exhaust to make it go fast (so that the plane can be pushed ahead by the reaction force). They produce very little power, just enough to power the Auxiliary Power Unit (that manages the plane electronics, air-conditioning etc.). If you want to use a gas turbine for produci…

Other people have already mentioned the distinction between turbojets (what you’re describing) and turbofan engines, but I think there’s another inaccuracy: > They produce very little power, just enough to power the Auxiliary Power Unit (that manages the plane electronics, air-conditioning etc.). The APU is a completely separate gas turbine that doesn’t rely on the main engines. As a consequence, the APU on an airpla…

It's because to extract all the energy from the exhaust, you need huuuuuge turbine blades to extract the last little bit of energy from very slow moving air.

So instead you extract most of the energy, and then use the last little bit as extra thrust in a plane/helicopter.

Re: Mazda’s rotary engine in the age of the electric car

#149

Post by dkjaudyeqooe »

Prcmaker wrote: post #128
porphyra wrote: post #36

Earlier quoted context omitted.

Sports cars, in general, are much loved but seldom bought.

I'm literally waiting for it, have been for quite a while. Small cars have numerous benefits over just being sporty. An electric, or even a hybrid 86/BRZ or miata would be great, but can't be compared to the mini or fiat, and while tesla might be fast, it's huge. Even with a price increase these could be more affordable than a lot of sports cars. The 86/BRZ has been a huge seller too.

The EV market is so frustrating right now. Everything seems to more or less be an SUV.

I wish someone would deliver something small, light, aerodynamic, stripped down and without features of marginal utility. Sportiness sort of comes for free.

The only important features for an EV are (excluding safety issues) are change speed and range. I might add a heat pump for the cabin (and battery in cold climes). Skip the screen and just let me use my phone and give me physical controls.

If a car marker thought seriously for a moment and resisted the full techno wank that is inflicted upon us at the moment, they'd make a lot of money.

It's a car, it's not that complicated, get back to basics.

Re: Mazda’s rotary engine in the age of the electric car

#150

Post by interstice »

pavlov wrote: post #131
486sx33 wrote: post #2

Does it produce more low end torque verses a traditional gasoline combustion engine? If not then why is it better suited for electrical generation? Is it more efficient with less load? The article mostly makes it sound like Mazda just loves the wankle and wants to find any possibly way to bring it back - even though it has “high” emissions… so coupling it with a hybrid electric motor makes it happen.. That can’t be t…

It can be the whole story. Engineering organizations fall in love with superficial attributes of solutions that worked especially well for them in the past. When RIM/BlackBerry realized the iPhone was a serious threat, they built a touchscreen phone where the entire display produces a physical clicking effect because they were so convinced that what people really want from a smartphone is the click of a keyboard. Maz…

Since the achilles heal of the rotary is wearing seals has anyone seriously invested in testing coating/material tech for this? It may not make sense for mass production but spending ~10k to make a bulletproof rx7 would be an incredibly good investment.
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